The present invention relates to surface interference detectors.
Many technologies require working surfaces with a controlled level of surface protrusions. For example, thin film heads are intended to fly over recording disks in very close proximity to the disk surface. A head/disk interference (HDI) occurs when the flying head interferes or impacts with a disk surface protrusion, such as foreign matter on the disk surface or a raised portion of the disk surface. Typical limits on acceptable hard disk surface protrusions are on the order of several microinches.
Disk surface protrusions are conventionally detected with a piezoelectric crystal transducer mounted on a test head flying over the disk of interest. A protrusion which does not extend up to flying height will not generate a transducer signal because it will not interfere with the head. When an HDI occurs, an interference signal is generated by the transducer. If the interference signal exceeds or satisfies a background noise threshold, or some multiple of this signal, then an interference is indicated. Conventional HDI detectors read the peak on the interference signal and employ statistical averaging to achieve an acceptable credence (believability) level. Hence, in practice, a disk is submitted to several revolutions of credence checking in order to verify an interference indication.